Smart ways to help reduce bycatch and make oceans healthier

While the world’s growing appetite for seafood may be good news for the fishing industry, overfishing is endangering some marine species and driving others to the verge of extinction.

Many sharks, rays and marine mammals like turtles become ensnared in fishing nets or hooked on long lines. Some will be discarded overboard as unintended bycatch, others will be treated as untargeted secondary catch, and stowed in a fishing vessel’s hold and taken to market.

Fishery catches have increased five-fold over the last 70 years. A United Nations Food and Agriculture Organization report – The State of World Fisheries and Aquaculture 2020 – shows global fishing intensity has increased from 17 million tonnes in 1950 to 84 million tonnes in 2018. An increase that places a heavy burden on marine life that is caught accidentally.

But technology is helping create smart solutions to help reduce the volume of unwanted and untargeted fish and mammals caught by the global fishing industry.

Illuminating the bycatch problem

Fitting lights to fishing gear has been found to reduce the number of marine creatures caught as bycatch, making fishing more sustainable.

Gillnets are among the most widely adopted methods used by small-scale fisheries, which are either attached to the ocean floor or released by trawling vessels to drift along and catch fish. Usually, anything and everything that swims through them becomes ensnared, including non targeted big fish and large marine creatures that can drown trying to free themselves.

Scientists from the University of Exeter and Peruvian NGO ProDelphinus, attached LED lights at intervals along gill nets which, particularly at night, act as a visual warning to help would-be bycatch avoid nets.

A study of more than 860 fishing trips over a three year period, found that gillnets with lights attached resulted in a reduction of up to 74.4% in sea turtle bycatch and up to 70.8% in small cetaceans like dolphins and porpoises. The method is cheap, easy to implement and produced no recorded reduction in the number of fish caught. In some instances the catch increased.

Safeguarding seabirds

Creative solutions can also help longline fisheries prevent seabirds swooping for food and accidentally getting hooked.

Hundreds of thousands of seabirds are accidentally killed by long line fishing each year, including tens of thousands of albatrosses, according to global conservation partnership BirdLife International.

One countermeasure that has been in use for some time is Tori lines, which act as a kind of marine scarecrow. While long lines are set beneath the water line to fish, a line with tassels attached at intervals is towed above the water line to attract seabirds and distract them from diving for food.

Hookpod is a more sophisticated solution. It involves a device that attaches to long lines forming a case around the fishing hook. The device sinks with the baited line beyond the normal diving depth of most seabirds, where the hook is automatically released to begin fishing.

If seabirds swoop to feed on the bait as it sinks, they avoid being accidentally hooked as the barb is enclosed in the device.

An escape route for marine creatures

Providing an escape route for trapped marine animals is another option. The US National Oceanic and Atmospheric Administration (NOAA) is working with the shrimp industry to do just that.

Shrimp fishing poses a major threat to sea turtles. Many are accidentally caught in nets and dragged through the water, where they drown from being unable to reach the surface to breath. But the addition of a Turtle Excluder Device could offer a solution, creating an escape hatch in shrimp nets.

A grid of bars across the center of the net is big enough for shrimps to pass through, but too small for turtles and other large animals. Instead of ending up in the net, turtles can swim through a hole to freedom.

”Because they behave differently to shrimps, turtles and big animals like swordfish get ejected out of the net, whereas the prawns will still be caught, helping to reduce bycatch," says Andy Cornish,leader of the World Wildlife Fund’s ‘Sharks: Restoring the Balance’ conservation programme.

“We need to continue finding ways that commonly used types of fishing gear can catch the target species, but catch less sharks, rays and other fish and marine mammals,” he adds.